Nitric oxide synthase expression in Pseudomonas koreensis MME3 improves plant growth promotion traits

Abstract

The development of novel biotechnologies that promote a better use of N to optimize crop yield is a central goal for sustainable agriculture. Phytostimulation, biofertilization, and bioprotection through the use of bio-inputs are promising technologiesfor this purpose. In this study, the plant growth–promoting rhizobacteria Pseudomonas koreensis MME3 was geneticallymodifed to express a nitric oxide synthase of Synechococcus SyNOS, an atypical enzyme with a globin domain that convertsnitric oxide to nitrate. A cassette for constitutive expression of synos was introduced as a single insertion into the genomeof P. koreensis MME3 using a miniTn7 system. The resulting recombinant strain MME3:SyNOS showed improved growth,motility, and bioflm formation. The impact of MME3:SyNOS inoculation on Brachypodium distachyon growth and N uptakeand use efciencies under diferent N availability situations was analyzed, in comparison to the control strain MME3:c.After 35 days of inoculation, plants treated with MME3:SyNOS had a higher root dry weight, both under semi-hydroponicand greenhouse conditions. At harvest, both MME3:SyNOS and MME3:c increased N uptake and use efciency of plantsgrown under low N soil. Our results indicate that synos expression is a valid strategy to boost the phytostimulatory capacityof plant-associated bacteria and improve the adaptability of plants to N defciency.